A conductive heating method, a dielectric heating method, and an induction heating method are well known as methods for electrically heating a food material, for example. Among them, the conductive and dielectric heating method conduct heating by the heat generated by the material (food) itself and are significantly different from the induction heating method by which heating is conducted by using Joule heat generated inside the metal container by a induced current (eddy current). In the case of the conductive heating method, the electric current directly flows in food and it is necessary to bring the upper and lower electrodes into contact with the food. In this case, where the food does not have a uniform thickness, there are zones on the food surface that are in contact with food and those that are not. The contactless zones are unevenly heated and are not heated sufficiently, whereas the contact zones can be overheated, that is, excessively heated. In the case of dielectric heating, the electric current does not flow directly through food, but where the food thickness is not uniform, both of the electric field intensity and dielectric constant differ significantly between zones that are in contact with the electrodes and those that are not, causing problems similar to those encountered in the conductive heating method. A conductive heating device is known (see, for example, Patent Document 1) in which in order to heat uniformly such food of irregular shape that has uneven thickness, an electrolytic solution is sprayed over the food surface to form a thin electrolyte film, a flexible electrode having good electric conductivity, composed of a flexible member, for example, a metal foil such as titanium, aluminum, iron, platinum, and stainless steel, and formed in a split-curtain-like shape suspended from a frame is used as the upper electrode, the upper electrode can be moved in the vertical direction, and the height of the upper electrode can be adjusted, thereby making it possible to conduct uniform heating of thick and thin portions of the food. A similar conductive heating device for food is also known (see, for example, Patent Document 2) in which the upper conductive portion (upper electrode) is composed of a supply tank that supplies an electrolytic solution and a flexible split-curtain-shaped conducive brush that hangs down from the supply tank, wherein the electrolyte drops or flows down onto the food through the brush. Further, a method for manufacturing a sterilized solid food product is known (see, for Example, Patent Document 3) by which a solid food product is tightly packaged with a packaging material to form a package, the package is disposed in a fluid body inside a pressure variable container, and a high-frequency electric field is applied to the container to conduct dielectric heating of the package.    Patent Document 1: Japanese Patent Application. Laid-open No. 2003-47413.    Patent Document 2: Japanese Patent No. 3352388.    Patent Document 3: Japanese Patent No. 3604109.
Furthermore, heating electrodes that are disposed opposite each other and are used to electrically heat material are known from JP 2007/159413. These electrodes are supported by a support means and axially slidable within the support means. With the pin displacement means the pin electrodes are axially displaceable.